In a Connections environment, where you have changed the permissions so that only authenticated users can use Connections (by setting all "reader" roles in all Websphere applications to "All Authenticated in Application's Realm"), you are no longer able to use the Rich Content app within a Community.
If you add the app to the Community you see the message "The page could not be created due to an error".
To solve the issue, set the role "reader" for the WAS application "RichTextEditor" back to "Everyone". This application does, by default, not allow anonymous access so that this is not a problem.
After restarting the application, your "Rich Text" app should work as normal.